In published German application Offenlegungsschrift 2,234,368 (see U.S. Pat. No. 3,803,809) and elsewhere, there are described dust-collecting electrostatic precipitators which comprise a housing traversed by the dust-carrying gas stream and provided with a multiplicity of transversely spaced mutually parallel collector-electrode walls which define between them the gas channels. Corona-discharge electrode arrays are generally provided between the collector-electrode walls and a rapping device can be provided to cause collected dust to shed from the collector electrodes and be deposited, in turn, in bins at the base of the precipitator.
In the latter disclosure, the collecting electrodes are made up of individual collecting electrode strips whose adjacent side edges are hooked loosely one into the other and whose tops are all fixed to a common carrier while the bottom ends are tied to a rapping linkage, bar or member which receives the rapping impact. The exposed edges of the end strips of the collecting-electrode walls are, in turn, held against rotation by profile supporting members which embrace these edges or are locked to them in the manner of the edge interlock between adjoining strips, and extend throughout the height of the latter.
This design of the end strips and of the collecting electrode walls or strips has proved to be of advantage in reducing the distortion of the collecting electrode walls in the case of flameless combustion at the gas/solid interface on the collecting electrodes.
Flameless combination phenomena have been encountered recently with increasing frequency, especially in iron-ore sintering plants, the flameless combustion being caused by the feeding of oil-containing additives, such as rolling-mill scale, to the sintering machines.
Unless the oily substance is burned off completely in the sintering bed, there is some distillation of hydrocarbons which are entrained in the exhaust gases and result in a flameless combustion on the collecting electrodes, particularly during initiation of operation of the electrostatic precipitator or upon termination of operations therewith.
The flameless combustion of hydrocarbons or the like at the aforementioned interfaces can result in local overheating of the collecting electrodes. Since the latter are most frequently cold-rolled profile sheet elements, the heating can result in relieving of internal stresses, thereby causing distortion of the strips. The local distortion may be in the form of bulges or the like.
It has been proposed to eliminate such bulges or to reduce them (printed German Pat. application 2,118,803) by altering the ratio of the width of the collecting electrode to its height. To this end, the strips are divided and the parts of each strip are arranged one above the other and are interconnected by straps or the like. This system is highly expensive and involves the disadvantage that during assembly of the wall or repairs thereof, the strips cannot simply be lifted out of the precipitator but require substantial disassembly of the apparatus and even separation of the parts of the subdivided strips.
Even when the collecting electrode strips are located by lateral profiled supporting members provided at the leading and trailing ends of a collecting electrode wall, as taught in U.S. Pat. No. 3,803,809, a bulging of the collecting surfaces in the plane of the wall cannot be entirely eliminated. A reduction of the discharge gap will reduce the highest permissible voltage which may be obtained so that the efficiency of dust/gas separation will be reduced. Whereas the loose hooking of each electrode strip into an adjacent one in an electrode wall has an equalizing influence too, this influence is not sufficient in electrode walls having dimensions such as are now used, i.e., a height of 10-15 meters, a width of 6 meters, and an area of 30-90 m.sup.2 per electrode wall consisting of about 12 collecting electrode strips.